Me spending 20 minutes crouched in a bush muttering cloud names to myself while the actual sunset happens behind me is a real thing that has happened. Your grandpa sounds like he knew what was up. The best shots I've ever gotten were the ones where I just stood there like a goofball and let it happen.

Did your uncle actually pour a full slab, or did he do it in sections with control joints cut in? Because that makes a huge difference in my experience. Concrete that size will crack somewhere, it's just a question of where, and control joints are what tell it where to crack so it stays hidden. If his has zero cracks after 25 plus years with no joints, that's honestly pretty rare and I'd want to see it before believing it. Pavers do shift and let weeds through if the base wasn't done right, that part is true, but a bad concrete pour can heave and crack too, so it's not automatically the better choice. Take this with a grain of salt, I'm just a guy who's messed up both kinds of patios.